<select class="input20" name="cardpostalcode" id="cardpostalcode"  onchange="showCity(this.value);">
    <option value="">Select a Postal code</option>
    {section name=i loop=$postalcodeArr}
    <option value="{$postalcodeArr[i].postalcode}">{$postalcodeArr[i].postalcode}</option>
    {/section}
</select>